The management of normal pressure hydrocephalus (NPH) is challenging due to diagnostic uncertainties and high treatment risks. To date, there are no evidence-based treatment guidelines for this disorder. Our long-term goal is to improve the outcome of NPH by lowering complications related to shunt valves and by increasing our understanding of how different shunt designs influence cerebrospinal fluid (CSF) hydrodynamics. This investigation uses a three-tiered shared-subject study design. The Specific Aims are to 1) determine which of two adjustable valve designs, one with a siphon control device and one without, is superior for the treatment of NPH with regard to lowering the complication rate, 2) compare the intracranial pressure (ICP) physiological response of a standard differential pressure valve, with and without a siphon control device, in the treatment of NPH, and 3) determine whether intracranial hemo/hydrodynamic variables, measured before and after a shunt operation, support the tuned-dynamic absorber model, of intracranial pressure dynamics. We hypothesize that siphon control devices increase the incidence of shunt under-drainage, manifesting as a lack of both neurological improvement and ventricular size reduction. Furthermore, we hypothesize that current hydrocephalus models are over- simplistic and that shunt-induced hydrodynamics are better modeled based on ICP waveform characteristics and the application of novel dynamic models. All of the studies will be performed as part of a prospective, randomized clinical trial assessing two existing, FDA-approved, adjustable valves. The outcome analysis will be useful for clinicians wishing to apply evidence-based guidelines in the management of NPH. From a viewpoint of better understanding the ICP physiology of CSF shunts, the comprehensive hydrodynamic studies will provide valuable information that will be useful in selecting the optimal valve pressure or type for individual patients. In addition, we foresee the information being used by shunt valve manufacturers to improve current valve designs. Documenting definitive evidence of the tuned-dynamic absorber model could have fundamental implications to all ICP disorders.